Early television sets were quite fiddly. And I was forbidden to operate anything other than the on-off-volume knob and the tuner knob. There was a little door that hid the real controls that let you adjust the vertical and horizontal aspects, contrast and brightness.
And then there were the test patterns. There were the regular test patterns:
And then there were the “uh-oh we’re having a problem” test patterns:
Mary Sue and Her WayBack Machine 